To remove the paint, dirt or other surface coatings from a substrate such as a surface to be painted or cleaned, a blasting system is desirable and effective. There are a variety of blasting processes for these purposes, including, but not limited to, water blasting, dry abrasive blasting, and wet abrasive blasting. In certain applications, abrasive blasting systems are able to efficiently clean or remove a coating without damaging the underlying metal or other substrate; although in other applications, a certain degree of surface roughening may be desired.
The use of dry abrasive blasting with particles, such as those used in conventional sand blasting, may result in surface roughening. Typical blast particles are hard and abrasive in order to increase the efficiency of the blasting operation but may, therefore, result in damage to the substrate. Soft recyclable blast particles are sometimes substituted to avoid surface damage. These recyclable blast particles include, but are not limited to, agricultural products such as crushed walnut shells, crushed pistachio shells, corn husks, and rice hulls. Plastic particles are also sometimes used to reduce substrate surface damage but may also result in a reduction in efficiency of the blasting operation.
Wet abrasive systems have been used to also control and reduce surface damage. Wet abrasive systems combine the benefits of water blasting systems with dry abrasive blasting systems. In wet abrasive blasting, the fluid encapsulates particles of the abrasive media to simultaneously add mass to the abrasive and buffer the impact of the abrasive against the substrate to reduce potential surface damage. The encapsulated media still effectively strips or cleans the surface while the water also reduces the dust produced by dry blasting. However, wet abrasive systems require efficient delivery and mixing of a slurry stream with a pressurized gas stream to produce a consistent three-phase blast stream comprising a three-phase mixture of fluid, solid abrasive, and gas. If the mixing of slurry and pressurized gas is not well controlled, the blasting process is less efficient and, therefore, the benefits of the wet abrasive system are not fully realized.
Wet abrasive blasting systems typically comprise an air supply pressure regulator that may be adjusted to set the blast pressure. Typically, in a wet abrasive blast system, the blast pressure is defined as the pressure of the air supply upstream of the mixer. The air supply pressure regulator may be adjusted higher for a more aggressive blast process or adjusted lower for a less aggressive blasting operation. A less aggressive blasting process may be used for removing softer coatings or to prevent damage of softer or more vulnerable substrates from damage. However, in most cases, the blast pressure cannot be adjusted independently while maintaining an efficient blasting operation. A slurry flow control valve and/or a blast pot pressure must also be properly adjusted to provide a proper three-phase blast stream to the blast nozzle. However in operation, if the pressure and flow adjustments are not properly made, especially by inexperienced or under-trained operators, the blast process becomes inefficient, takes longer time to complete, and uses more blast media and/or water than necessary.
There is a need for a wet abrasive system that is easier to control in order for the benefits of a wet abrasive system to be more fully realized. In the past, the control has been overly complicated and required extensive training before an operator became fully proficient. Even then, there remained the possibility of operator error because operators do not understand the fluid dynamics of a wet abrasive system. The pressure setting of the blast pot or the blast pressure may be incorrectly set relative to the other pressures of the wet abrasive system.